The present invention relates to an obstacle detecting apparatus equipped in an automotive vehicle to detect an obstacle and generate an alarm when the obstacle is within a warning distance.
FIG. 5 is a circuit block diagram showing a conventional obstacle detecting apparatus which comprises a plurality of ultrasonic sensors 11, 41, 51 and 61, each serving as obstacle detecting sensor, provided at predetermined positions (e.g., front and rear bumpers) of an automotive vehicle. An electronic control unit (hereinafter, abbreviated ECU) 1, acting as central control apparatus, is connected to the ultrasonic sensors 11, 41, 51 and 61 via lines 70, 80, 90 and 100, respectively, so as to form a star connection pattern.
The microcomputer 2, equipped in ECU 1, executes the obstacle detecting processing when the shift position 72 of an automatic transmission (not shown) of an automotive vehicle is in one of the shift positions of R(reverse), D(drive), 2(second) and L(low) and when the vehicle speed 73 is equal to or less than 10 km/h.
First, the microcomputer 2 sends a transmit SW signal to analog switch 4 and a receive SW signal to analog switch 7. In response to these signals, both the analog switch 4 and analog switch 7 establish the lines connecting microcomputer 2 to ultrasonic sensor 11.
Next, the microcomputer 2 controls transmission driver 3 to generate an ultrasonic wave pulse (e.g., 10 consecutive rectangular waves of 40 kHz). Furthermore, the microcomputer 2 produces a threshold (voltage) 8 which is applied to one terminal of comparator 6. The threshold 8 determines a level for judging an obstacle. The comparator 6 has another terminal for receiving a sensor signal obtained from ultrasonic sensor 11. The comparator 6 compares the entered sensor signal with the given threshold.
The ultrasonic wave pulse, generated by transmission driver 3, is sent to ultrasonic sensor 11 via analog switch 4 and line 70. The ultrasonic sensor 11 comprises transmitting circuit 12, receiving gain adjusting section 13, and amplifier 14. When the ultrasonic wave pulse is entered into ultrasonic sensor 11, the transmitting circuit 12 emits a ultrasonic wave via a microphone 15. When any obstacle is present in a predetermined sensing area of ultrasonic sensor 11, the microphone 15 receives a reflected ultrasonic wave returning from this obstacle. The reflected ultrasonic wave, received by microphone 15, is amplified by amplifier 14 and is then entered into receiving gain adjusting section 13 to adjust the gain of reflected ultrasonic wave. The sensor signal, i.e., the reflected ultrasonic wave signal thus adjusted, is then sent to ECU 1 via line 70.
In ECU 1, the received sensor signal is entered into comparator 6 via analog switch 7 and receiving gain adjusting section 5. The comparator 6 compares the entered sensor signal with the threshold 8 given from microcomputer 2. When the sensor signal is larger than the give threshold 8, the comparator 6 sends an obstacle detection signal to microcomputer 2. The microcomputer 2 performs measurement of time which starts upon transmission of the ultrasonic wave and is up at entry of the obstacle detection signal. The microcomputer 2 converts the measured time into a corresponding distance of an obstacle. When the distance of the obstacle is within a predetermined warning distance, the microcomputer 2 generates an alarm.
After finishing the processing in the ultrasonic sensor 11, similar processing is performed successively for each of other ultrasonic sensors 41, 51 and 61 although a predetermined dormant period is provided. This dormant period is equivalent to a time required for eliminating adverse influence of multipath reflection waves caused by the obstacle or other objects (e.g., roads etc.). Hereinafter, this dormant period is referred to as multipath duration.
Relying only one judgement is not preferable to eliminate any possible error detection. Thus, the alarm is generated only when the obstacle detection signal is repetitively entered. The position of the detected obstacle is indicated in relation to the ultrasonic sensor having detected this obstacle, for example, on an LCD display installed on a dashboard. When the detected distance of the obstacle is in the range from 20 cm to 50 cm, an alarm indicator flickers with intermittent sound. When the detected distance of the obstacle is shorter than 20 cm, the alarm indicator continuously turns with continuous sound.
However, according to the above-described prior art, only ECU 1 has calculating function and this will cause various problems. For example, the signals sent from respective ultrasonic sensors 11, 41, 51, and 61 to ECU 1 are weak analog signals of several mV which are poor in noise durability. When such weak analog signals are sent from respective sensors provided at the front and rear bumpers of the automotive vehicle to ECU 1 via the long signal transmission path of lines 70, 80, 90, and 100, various electromagnetic noises may be superposed during the propagation of the signals via the lines 70, 80, 90 and 100 and will be erroneously recognized as the obstacle detection signal.
Furthermore, the signals detected by respective ultrasonic sensors 11, 41, 51, and 61 are collected and calculated in ECU 1. This will increase the calculation or computation load of ECU 1.
Furthermore, the ultrasonic sensors 11, 41, 51, and 61 are activated one by one with sufficient time intervals so as to eliminate the influence of multipath reflection waves which are produced by obstacles and other objects (e.g., road). This will require a long time to detect the obstacle. Issuance of alarm will be delayed, correspondingly.
The microphones 15 of respective ultrasonic sensors 11, 41, 51, and 61 are usually mass produced with manufacturing differences or variability in the oscillation frequency as well as in the sound pressure level. Thus, there is the possibility that ECU 1 may not have functionally good correspondence with each of other mass-produced individual ultrasonic sensors. The installation position and angle of respective ultrasonic sensors 11, 41, 51, and 61 are different in each type of automotive vehicles. Accordingly, it is necessary to perform the adjustment of receiving gain for each of respective ultrasonic sensors 11, 41, 51, and 61. Furthermore, the microphone 15 will require severe spec. Furthermore, it is necessary to differentiate the threshold 8 for each of the respective ultrasonic sensors 11, 41, 51, and 61 or for each type of automotive vehicles.